Electronic circuit arrangement for receiving low frequency electro-magnetic waves with an adjustable attenuator element

ABSTRACT

An electronic circuit arrangement for receiving low-frequency electromagnetic waves is proposed, having an inductor (L) acting as an antenna for generating a received signal, having a first receiver ( 2 ), connected to the inductor (L), for decoding a first component of the received signal and having a second receiver ( 3 ), connected to the inductor (L), for decoding a second component of the received signal, wherein at least the second receiver ( 3 ) is connected to the inductor (L) via an attenuator element ( 4 ) having adjustable attenuation, wherein at least one adjustment signal generation circuit ( 5, 6 ) is provided for generating an adjustment signal corresponding to a voltage of the received signal which is fed to the attenuator element ( 4 ) for adjusting the attenuation.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the National Phase Application under 35 USC §371 ofInternational Application No. PCT/EP2011/067018, filed Sep. 29, 2011,titled “Electronic Circuit Arrangement for Receiving Low FrequencyElectro-Magnetic Waves with an Adjustable Attenuator Element”, whichclaims priority to German Patent Application 10 2010 044 028.0, filedNov. 17, 2010, the subject matter of which is incorporated herein byreference.

BACKGROUND

A. Technical Field

The present invention relates to an electronic circuit arrangement forreceiving low frequency electromagnetic waves, having an inductor actingas an antenna for generating a low frequency receive signal, having afirst receiver connected to the inductor for decoding a first componentof the receive signal and having a second receiver connected to theinductor for decoding a second component of the receive signal.

B. Background of the Invention

From current practice an electronic circuit arrangement for receivinglow frequency electromagnetic waves is known, having an inductor actingas an antenna that generates a low frequency electrical receive signal,corresponding to the received electromagnetic waves, that is fed to aplurality of differently designed receivers for decoding, so that onlyone inductor is necessary for a plurality of receivers. Decoding isunderstood here to be processing of the receive signal so that usefulinformation can be extracted. In this case, the receivers can be builtso that each of them processes a specific component of the receivesignal. In this manner, a significant space saving can be obtainedcompared to solutions in which each receiver has its own antenna. Thisapplies particularly in the low frequency range, which is understood tobe a frequency range from 20 kHz to 250 kHz, because the inductorssuited for this range have a considerable size.

However, if the components of the receive signal to be processed by thedifferent receivers have very different voltage values, it is possiblethat the voltage resistance of one of the receivers is such low that itis damaged by the component of the receive signal intended for anotherreceiver. This can occur in particular when the components trace back todifferent transmitting devices.

SUMMARY OF THE INVENTION

The object of the invention is to provide an electronic circuitarrangement of the named type in which the risk of damaging one of itsreceivers is reduced.

The object is attained with an electronic circuit arrangement of theinitially named type in which at least the second receiver is connectedto the inductor via an attenuator element having adjustable attenuation,wherein at least one adjustment signal generation circuit is providedfor generating an adjustment signal that corresponds to the voltage ofthe receive signal and that is fed to the attenuator element foradjusting the attenuation.

Here, an attenuator element is understood to be an element whichreduces, in an essentially frequency independent manner, the voltage ofthe received electrical signal that is fed to it, and thus generates anattenuated receive signal that contains essentially the sameinformational content. The attenuation of the attenuator element isadjustable and specifies the level of the attenuation of the receivesignal. It can be expressed in decibels, for example.

It is provided that an adjustment signal is generated by means of anadjustment signal generation circuit, and that this generated signalcorresponds to the voltage of the receive signal. The adjustment signalis fed to the attenuator element so that its attenuation variesdepending on the voltage of the receive signal, wherein in particular,the attenuation also increases with increasing voltage.

Damage to the second receiver by voltages that are too high can now beeffectively avoided by at least the second receiver, in particular areceiver having a higher sensitivity and/or having a lower voltageresistance than the first receiver, being loaded via the attenuatorelement with an attenuated receive signal. In particular, components ofthe receive signal that have a high voltage and that are provided fordecoding by the first receiver cannot thus cause any damage, because attheir input the attenuation can be adjusted to be sufficiently high thatthe voltage of the receive signal is not harmful.

If, on the other hand, a component of the receive signal is present thatis provided for decoding by the second receiver and in particular has alow voltage, the attenuation can be reduced so that decoding the receivesignal is still possible. The overall sensitivity of the second receiveris therefore essentially maintained.

One of the receivers, or both receivers, can have differential inputs. Adifferential input is understood to be a two-pole input whose two polesare connected neither to a positive nor to a negative supply potentialof a supply voltage supplying the circuit. In the context of the presentapplication, “connected to” is understood to be “electricallyconductively connected”, unless specified otherwise.

According to an advantageous further development of the invention, theelectronic circuit arrangement is implemented as a CMOS integratedcircuit. A particularly reliable and space saving construction can berealized in this manner.

An integrated circuit is understood to be an electronic circuitcomprising a plurality of electronic components and the associatedwiring that are implemented on a common substrate, also called a chip. Afully integrated design can be provided in which all electroniccomponents are disposed on exactly one substrate.

Furthermore, the circuit according to the invention is manufactured inCMOS technology, where it is understood that PMOS transistors, alsocalled p-channel metal oxide semiconductor transistors, as well as NMOStransistors, also called n-channel metal oxide semiconductortransistors, can be disposed on a common substrate.

According to an advantageous further development of the invention, thefirst receiver is a transponder that generates from the receive signal aresponse signal that can be emitted via the inductor. The transpondercan be a component of an RFID system, which performs automaticidentification, in particular, of people as part of an access controlprocess, for example, in a motor vehicle. For example, a reading devicedisposed on a motor vehicle can emit an query signal that is decoded bythe first receiver and is responded to with the indication of anidentity. If a permitted identity is sent, the vehicle can then beopened.

In particular, when the first receiver is an RFID transponder, theadvantages of the invention become evident, because here the voltage ofthe receive signal generated by the query signal depends strongly on thechanging distance between the reading device and the electronic circuit.In practice, such a system is designed so that it can have an operatingrange of several meters. At the same time however, it cannot be excludedthat the actual distance only amounts to a few centimeters. The receivesignal can then attain such a large voltage that in principle, it coulddamage, in particular, the second receiver. However, this is effectivelyavoided by the design of the circuit according to the invention.Although known RFID transponders are sufficiently voltage stable inorder to withstand the possible voltages of the receive signal, it is inprinciple also possible to protect the first receiver with an attenuatorelement of the described type.

According to an expedient further development of the invention, thetransponder is a passive transponder. Passive transponders obtain theenergy required for their operation from the query signal which isespecially powerful for this purpose. Specifically in this case, damageto the second receiver can be avoided.

According to an advantageous further development of the invention, thesecond receiver is a wake-up receiver that, depending on the receivesignal, switches an electronic component that is in standby mode into anoperating mode. A wake-up receiver is understood to be a receiver thatupon receipt of a predefined signal switches an electronic component,for example a transmitter, from standby mode into operating mode. Inthis manner, the energy consumption of the electronic component issignificantly reduced when it is not required, that is, in particular,before receipt of the predefined signal. In this case, the predefinedsignal can be emitted by a so-called wake-up transmitter, wherein itshould be received at large distances even if the transmitter has lowpower. Therefore, wake-up receivers are typically designed for decodingreceive signals that have a lower voltage than is typical in RFIDtransponders. At the same time, wake-up receivers are as a rule lessvoltage-resistant than RFID transponders. For example, the voltageresistance of a wake-up receiver can amount to a few hundred millivolts,whereas the voltage resistance of the RFID transponder can amount to afew volts. Therefore, the circuit according to the invention isparticularly advantageous when it comprises an RFID transponder and awake-up receiver protected by the attenuator element.

According to an advantageous further development of the invention, theadjustment signal generation circuit comprises a voltage limiter forlimiting the voltage of the adjustment signal. A voltage limiter isgenerally understood to be an electronic component that reduces thevoltage if it exceeds a defined threshold value. In this manner, even inthe case of a particularly high voltage of the receive signal, damage tothe attenuator element and/or other components of the circuit can beavoided by means of the adjustment signal.

According to an advantageous further development of the invention theadjustment signal generation circuit comprises a rectifier circuit forrectifying the receive signal. By means of this, an adjustment signalthat is suitable for adjusting the attenuation of the attenuator elementcan be generated in a simple manner.

According to an advantageous further development of the invention, therectifier circuit has at least one MOS transistor, in particular an NMOStransistor, in which a gate terminal is connected with low impedance toa drain terminal, so that it functions as a diode. In this manner, therectifier circuit can be implemented as a compact integrated CMOScircuit that is particularly simple to produce.

According to an advantageous further development of the invention, theattenuator element has a symmetrical voltage divider circuit, in which afirst side of the inductor is connected via a first capacitor, a secondcapacitor and via a first component arrangement having at least oneactive electronic component to a ground potential, wherein a second sideof the inductor is connected via a third capacitor, a fourth capacitorand via a second component arrangement having at least one activeelectronic component to a ground potential, wherein the attenuatedreceive signal is tapped between the sides of the first capacitor andthe third capacitor that face away from the inductor. In this context,an active electronic component is understood to be an electroniccomponent which depending on its wiring has an amplification and/orcontrol function.

The voltage of the attenuated receive signal tapped between first andsecond capacitor and between the third and fourth capacitor, depends onthe complex resistivity of the first and second component arrangements.This complex resistivity can be adjusted by the adjustment signal sothat the voltage of the attenuated receive signal lies in a safe range.

Due to the symmetrical design, especially relative to ground, of thevoltage divider, which in particular can mean that the first and thethird capacitor, the second and the fourth capacitor, as well as thefirst and the second component arrangement are identical to each other,it is possible to feed the attenuated receive signal directly to thedifferential input of the second receiver.

According to an advantageous further development of the invention, theactive electronic components are MOS transistors, in particular NMOStransistors. As a result, the attenuator element can be implemented asan integrated CMOS circuit that is particularly compact and easy toproduce.

According to an advantageous further development of the invention theadjustment signal is fed to at least one pair formed from a said activeelectronic component of the first component arrangement and a saidactive electronic component of the second component arrangement. As aresult, it can be attained in a simple manner that the attenuatedreceive signal is symmetrical with respect to the ground potential,independently of the respective adjusted attenuation.

According to an advantageous further development of the invention, theattenuator element has a first said pair for attenuating the receivesignal in a first voltage range, and a second said pair for additionalattenuation of the receive signal in a second, higher voltage range. Forthis, the receive signal is attenuated using two separately controllablepairs of active components, which means that the voltage range, in whichthe voltage of the receive signal can be reduced to a permissible value,can be very large. With this design, the adjustment accuracy can beimproved in the entire voltage range.

According to an advantageous further development of the invention afirst said adjustment signal generation circuit for generating a firstsaid adjustment signal is fed to the first said pair and a second saidadjustment signal generation circuit for generating a second setadjustment signal, which is fed to the second said pair. Thereby, thefirst adjustment signal as well as the second adjustment signal isgenerated such that it is optimally matched to the electrical propertiesof the respective pair of active elements. Thereby, the adjustmentaccuracy of the attenuation can be improved in the entire voltage rangeso that both over-attenuation as well as under-attenuation can beavoided.

According to an advantageous further development of the invention thefirst said adjustment signal generation circuit comprises a rectifiercircuit designed as a half-wave rectifier circuit. The adjustment signalgeneration circuit can be implemented very easily this way.

According to an advantageous further development of the invention thesecond said adjustment signal generation circuit comprises a rectifiercircuit designed as a full-wave rectifier circuit. Thereby, bothhalf-waves of a period of the receive signal can be considered whengenerating the adjustment signal.

According to a further advantageous development of the invention, thefull-wave rectifier circuit is employed for generating a supply voltagefor the passive transponder. In this manner, the full-wave rectifier canbe used simultaneously for multiple purposes, which overall simplifiesthe design of the circuit.

The advantageous embodiments and further developments of the inventiondescribed in the preceding and/or specified in the dependent claims,can—except for example, in the cases of explicit dependencies orincompatible alternatives—be used individually or also in any arbitrarycombination with each other.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and its advantageous embodiments and further developmentsand their advantages are described in more detail in the following basedon drawings. They show:

FIG. 1 a schematic circuit diagram of an exemplary embodiment of theelectronic circuit according to the invention, and,

FIG. 2 an exemplary embodiment of the diodes of the electronic circuitfrom FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an exemplary embodiment of the electronic circuit 1according to the invention that is designed for receiving low-frequencyelectromagnetic waves. The circuit 1 according to the invention isdesigned in an integrated construction, that is, as an integratedcircuit, which is understood to mean that a plurality of electroniccomponents and an associated wiring of the circuit 1 are implemented ona common substrate, also called a chip. Here, a fully integratedconstruction can be provided in which all electronic components of thecircuit are disposed on exactly one substrate.

Furthermore, the circuit 1 according to the invention is manufactured inCMOS technology, that is, a technology in which both PMOS transistors,also called p-channel metal oxide semiconductor transistors, as well asNMOS transistors, also called n-channel metal oxide semiconductortransistors, can be disposed on a common substrate.

The circuit 1 according to the invention has an inductor L, acting as anantenna, that together with a capacitor C7 forms an oscillator circuit.The oscil-latior circuit can have a resonance frequency, in particular,in the range of 20 kHz to 250 kHz. Using the oscillator circuit,received electromagnetic waves can be converted into an electricalreceive signal that is fed via electrical conductors directly to a firstreceiver 2. In the exemplary embodiment, the first receiver 2 is apassive transponder 2 that generates a response signal, depending on theinput signal, that can be emitted via the inductor L. The transponder 2can be a component of an RFID system, which provides an automaticidentification, in particular, of people, as part of an access controlprocess, for example, in a motor vehicle. In the exemplary embodiment,the RFID transponder 2 has a differential input for the received input.

Furthermore, a second receiver 3 is provided that is implemented as awake-up receiver 3. A wake-up receiver 3 is understood to be a receiverwhich, upon receipt of a predefined signal, switches an electroniccomponent, for example a transmitter, from a standby mode into anoperating mode. In this manner, the energy consumption of the electroniccomponent is greatly reduced when it is not needed, that is, inparticular, before receipt of the predefined signal. In this context,the predefined signal can be emitted from a so-called wake-uptransmitter, where it should be received at great distances even if thetransmitter has low power. Therefore, wake-up receivers 3 are typicallydesigned for decoding receive signals that have a lower voltage than istypical in RFID transponders 2. At the same time, wake-up receivers 3are as a rule less voltage-resistant than RFID transponders 2. Forexample, the voltage resistance of a wake-up receiver 3 can amount to afew hundred millivolts, whereas the voltage resistance of the RFIDtransponder 2 can amount to a few volts.

To prevent damage to the wake-up receiver 3 by a receive signal voltagethat is too high, an attenuator element 4 is provided with an adjustableattenuation. Here, an attenuator element 4 is understood to be anelement which reduces, essentially independently of frequency, thevoltage of the electrical receive signal that is fed to it, and sogenerates an attenuated receive signal that is fed to a differentialinput of the wake-up receiver 3. The attenuation of the attenuatorelement 4 specifies the level of the attenuation of the receive signal.

In the exemplary embodiment, the attenuator element 4 has a symmetricalvoltage divider circuit C3, C4, C5, C6, M1, M2, M3, M4 in which a firstside of the inductor L is connected via a first capacitor C3, a secondcapacitor C4 and via a first component arrangement M3, M4 having twoactive electronic components M3, M4, to the ground potential, wherein asecond side of the inductor L is connected via a third capacitor C5, afourth capacitor C6 and via a second component arrangement M1, M2 havingtwo further active electronic components M1, M2, to a ground potential.Here, the attenuated receive signal is tapped between the sides of thefirst capacitor C3 and the third capacitor C5 facing away from theinductor L.

The voltage of the attenuated receive signal tapped between the firstcapacitor C3 and the second capacitor C4, as well as between the thirdcapacitor C5 and the fourth capacitor C6, depends on the complexresistivity of the first component arrangement M3, M4 and the secondcomponent arrangement M1, M2. These complex resistivitities can beadjusted here by a first adjustment signal, which is generated by thefirst adjustment signal creation circuit 5, and by a second adjustmentsignal, which is generated by a second adjustment signal generationcircuit 6, so that the voltage of the attenuated receive signal lies ina harmless range.

Due to the symmetrical design, especially relative to ground, of thevoltage divider C3, C4, C5, C6, M1, M2, M3, M4, which in particular canmean that the first capacitor C3 and the third capacitor C5, the secondcapacitor C4 and the fourth capacitor C6, as well as the first componentarrangement M3, M4 and the second component arrangement M1, M2 eachcorrespond to each other, it is possible, to lead the attenuated receivesignal directly to the differential input of the second receiver 3.

The active electronic components M1, M2, M3, M4 of the attenuatorelement 4 are implemented in this exemplary embodiment as MOStransistors M1, M2, M3, M4, in particular NMOS transistors M1, M2, M3,M4.

In the exemplary embodiment, the first adjustment signal is fed to theactive electronic component M3 of the first component arrangement M3, M4and to the active electronic component M1 of the second componentarrangement M1, M2.

The jointly controlled active electronic components M1 and M3 form apair of active electronic components M1, M3 for damping the receivesignal in a first voltage range.

In the exemplary embodiment, the second adjustment signal is fed to theactive electronic component M4 of the first component arrangement M3,M4, and to the active electronic component M2 of the second componentarrangement M1, M2.

The jointly controlled active electronic components M2 and M4 form asecond pair of active electronic components M1, M3 for additionaldamping of the receive signal in a second, higher voltage range.

In this manner, the receive signal is attenuated by the use of twoseparate controllable pairs M1, M3, M2, M4 of active components M1, M3,M2, M4, whereby the voltage range, in which the voltage of the receivesignal can be reduced to a permissible value, can be very large.

By using two adjustment signal generation circuits 5, 6, both the firstadjustment signal and a second adjustment signal can be generated sothat they are optimally matched with respect to the electricalproperties of the respective pairs M1, M3, M2, M4 of active elements M1,M3, M2, M4. Due to this, the adjustment accuracy of the attenuation canbe improved in the entire voltage range so that both under-attenuationas well as over-attenuation can be avoided.

Due to the symmetrical pairwise arrangement and control of the activecomponents M1, M3, M2, M4 it can be attained in a simple manner that theattenuated receive signal is symmetrical with respect to the groundpotential, independently of the respective adjusted attenuation.

The first adjustment signal generation circuit 5 has a differentialinput for the receive signal, which is connected by two capacitors C1and C2 to the half-wave rectifier circuit D5, D6, D7. The half-waverectifier circuit D5, D6, D7 is comprised of a series connection ofthree diodes D5, D6, D7, wherein the capacitor C1 is connected to afirst connection of diodes D6 and D7. Furthermore, the capacitor C2 isconnected to a second connection of diodes D5 and D6. The firstadjustment signal is tapped here at one end of the series connection D5,D6, D7, whereas the other end of the series connection D5, D6, D7 isconnected to a ground potential. The voltage of the first adjustmentsignal is limited here with respect to ground by a voltage limiter 7.

The second adjustment signal generation circuit 6 has a differentialinput for the receive signal that is connected directly to a full-waverectifier circuit D1, D2, D3, D4. The full-wave rectifier circuit D5,D6, D7 is composed of four diodes D1, D2, D3, D4 which form a bridgecircuit. The voltage of the rectified receive signal is smoothed bymeans of a capacitor C8, and is limited by means of a voltage limiter 8.The rectified receive signal is fed to the transponder 2 as a supplyvoltage, and to the voltage detector 9, wherein the latter generates thesecond adjustment signal from the rectified receive signal.

FIG. 2 shows an exemplary embodiment of the diodes D1 to D7 of theelectronic circuit of FIG. 1. Here, the diodes D1 to D7 are eachcomprised of a MOS transistor, in particular, an NMOS transistor, inwhich a gate is connected with low impedance to a drain so that it actsas a common bipolar diode. In this manner, the rectifier circuits D1,D2, D3, D4, D5, D6, D7 can be implemented as integrated CMOS circuitsthat are compact and particularly simple to produce.

REFERENCE LIST

-   1 Electronic Circuit Arrangement-   2 First Receiver-   3 Second Receiver-   4 Attenuator Element-   5 First Adjustment Signal Generation Circuit-   6 Second Adjustment Signal Generation Circuit-   7 Voltage Limiter-   8 Voltage Limiter-   9 Voltage Detector-   L Inductor-   C1 . . . C8 Capacitor-   D1 . . . D7 Diode-   M1 . . . M4 Active Electronic Component, NMOS Transistor d Drain    Terminal-   g Gate Terminal-   s Source-Terminal-   Vref Reference Voltage

I claim:
 1. An electronic circuit for receiving low-frequencyelectromagnetic waves, the circuit comprising: an inductor acting thatgenerates a receive signal; a first receiver, coupled to the inductor,the first receiver decodes a first component of the receive signal; asecond receiver, coupled to the inductor, the second receiver decodes asecond component of the receive signal, characterized in that at leastthe second receiver is coupled to the inductor via an attenuator elementhaving an adjustable attenuation; and wherein at least one adjustmentsignal generation circuit generates an adjustment signal correspondingto a voltage of the receive signal, which is fed to the attenuatorelement for adjusting the attenuation.
 2. The electronic circuitaccording to claim 1, characterized in that electronic circuit isimplemented as a CMOS integrated circuit.
 3. The electronic circuitaccording to claim 1, characterized in that the first receiver is atransponder, which depending on the receive signal generates a responsesignal which can be emitted via the inductor.
 4. The electronic circuitaccording to claim 3, characterized in that the transponder is a passivetransponder.
 5. The electronic circuit according to claim 1,characterized in that the second receiver is a wake-up receiver, whichdepending on the receive signal, switches an electronic componentlocated in a standby mode into an operating mode.
 6. The electroniccircuit according to claim 1, characterized in that the adjustmentsignal generation circuit comprises a voltage limiter for limiting thevoltage of the adjustment signal.
 7. The electronic circuit according toclaim 1, characterized in that the adjustment signal generation circuitcomprises a rectifier circuit for rectifying the receive signal.
 8. Theelectronic circuit according to claim 7, characterized in that therectifier circuit has at least one MOS transistor, in which a gate iscoupled with a low impedance to a drain.
 9. The electronic circuitaccording to claim 1, characterized in that the attenuator elementcomprises a symmetrical voltage divider circuit, in which a first sideof the inductor (L) is coupled via a first capacitor, a second capacitorand via a first component arrangement having at least one activeelectronic component to a ground potential, wherein a second side of theinductor is coupled via a third capacitor, a fourth capacitor and via asecond component arrangement having at least one active electroniccomponent to a ground potential, wherein the attenuated receive signalis tapped between the sides of the first capacitor and the thirdcapacitor.
 10. The electronic circuit according to claim 9,characterized in that the at least one active electronic component is aMOS transistor.
 11. The electronic circuit according to claim 10,characterized in that the adjustment signal is fed to a first activeelectronic component within the at least one active electronic componentand to a second active electronic component within the at least oneactive electronic component.
 12. The electronic circuit according toclaim 11, characterized in that the attenuator element has a firsttransistor pair for attenuating the receive signal in a first voltagerange, and a second transistor pair for additional attenuation of thereceive signal in a second, higher voltage range.
 13. The electroniccircuit according to claim 12, characterized in that a first adjustmentsignal generation circuit generates a first adjustment signal that isfed to the first transistor pair, and that a second adjustment signalgeneration circuit generates a second adjustment signal that is fed tothe second transistor pair.
 14. The electronic circuit according toclaim 13, characterized in that the first adjustment signal generationcircuit comprises a rectifier circuit implemented as a half-waverectifier circuit.
 15. The electronic circuit according to claim 14,characterized in that the second adjustment signal generation circuitcomprises a rectifier circuit implemented as a full-wave rectifiercircuit.
 16. The electronic circuit according to claim 15, characterizedin that the full-wave rectifier circuit generates a supply voltage for apassive transponder.